The porous bottom culture dishes (PBCDs) and the devices for the sterile measurement of the electrophysiological parameter of cell layers which we developed are receiving wide application. In addition to the studies of kidney epithelial here at NIH and in more than 50 other laboratories in the U.S.A. and abroad, they are being successfully used in the study of pulmonary epithelia. We have shown that the electrophysiological responses A6 (Xenopus laevis kidney) cell layers are enhanced by increasing the exchange of nutrients and wastes at both the upper and lower surfaces by gently shaking the PBCD's in the incubator during the entire development of the cell layer and its Na transport capability. The major role played by Ca++ in the regulation of transport and other process in cells has prompted us to improve the methods of measuring Ca++ activity inside epithelial cells of many kinds. Microelectrodes need to be 0.1 or 0.2 microns in diameter to enter most epithelial cells without causing damage which makes reliabale readings impossible. It is logically argued that electrodes of this size have walls so thin that they are totally hydrated near the tip and with the monovalent ions of the glass become Na++ and k+ electrodes. This conflict between Ca++, Na+ and K+ sensitivities is believed to cause the poor performance often seen for electrodes smaller than 1 micron in diameter at Ca++ activities below 10 to the-6 molal. We have therefore designed, constructed, and used unique anular burners for making micropipettes form fused quartz. These fused quartz micropipettes are made from high purity material so that no metal ions will be present in the wall to give the completed microelectrodes unwanted ionic responses, It is expected that this will significantly improve the accuracy of intracellular Ca++ activity measurements of epithelial cells.